Field of the Invention
The invention relates to the field of electronic circuits, and specifically to a circuit configuration for measuring the resistance and/or leakage between two electrical nodes in an airbag control device.
Measurements of resistance and leakage resistance are frequently carried out by direct-current measurements. Since it is necessary to ensure an adequate signal/noise ratio, measurements are taken at high signal levels. This results in undesirably high electromagnetic radiation. Further, the required generators having a direct-current component and the required amplifiers are very expensive.
European Patent application EP A 0 689 058 discloses a circuit for monitoring an electrical circuit node for a fault condition in the form of a leakage resistance. The disclosed test configuration has a current source that is coupled to the node and an analyzer that has at least one comparator. A test current in the form of a direct current having a predetermined value is applied to one terminal of the circuit and only flows when the voltage between the node and the terminal drops below a predetermined limit value. Transgression of this voltage limit value by a leakage current leads to a change in the voltage at the comparator. A window comparator is preferably used to monitor the node for a leakage resistance with respect to each of two terminals of the circuit and a second current source having an opposite test current is provided.
German Patent Application DE-A 195 17 141 discloses a circuit for monitoring a priming-cap resistance of an airbag control device. A test current is alternately fed into the priming-cap resistance from mutually opposite directions. Each voltage value measured across the resistance is differentially amplified together with a positive reference voltage. A difference between the amplified voltages is calculated which is equal to a voltage value which would be caused by a test current having twice the level.